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Water-to-Air Ratio GreenRoofs101

Green Team at Green Roof Technology, - Tuesday, March 17, 2020

Why is AIR-to-WATER Ratio on Green Roofs so important?

The air-to-water ratio is the ratio between air and water in the pores of a media. (Download PDF: click here)

 

By Green Roof Expert Extraordinaire Jorg Breuning, March 2020

 

Introduction (Challenges)

On ground disconnected structures like roofs the available rooting space for plants is typically limited because of weight restraints. Additionally the Green Roof components and the plants are exposed to more extreme environmental impact like higher wind speeds, reflecting surfaces, higher temperatures, air pollution, artificial light at night, lower bio-diversity and more. Water to Air RatioIn such locations the Air-to-Water ratio within the Green Roof system can fluctuate much more often beyond the desired range what causes stress on the plants and stress on beneficial microbes. 

If more extremes are expected, selecting the right plants and right Green Roof system is crucial. In some cases an irrigation system (temporary or permanent) or enhanced drainage system should be considered to reduce stress conditions on the plants and to improve soil biology. However, operating an inappropriate irrigation system (like sprinklers) or drainage systems that were never engineered specifically for Green Roof applications can be counterproductive because the Air-to-Water ratio is not considered. Constant adverse Air-to-Water ratio is the problem on over 60% of the Green Roofs in North America and with changing weather patterns this problem is getting worse.

 

What is AIR-to-WATER RATIO (Introduction)

The vast majority of plants used on extensive or intensive Green Roofs thrive best within a specific Air-to-Water ratio range in the root zone of a Green Roof system. Over the course of a year and depending on weather conditions, a Green Roof system’s desirable the Air-to-Water ratio shall vary between 35/65 to 65/35 (65% water/35% air to vice versa). An Air-to-Water ratio in such a range is important for the resilience of plants, for nutrient exchange capacity, pH buffering capability, and beneficial (aerobe) microbes. Peaks in one or the other direction (adverse Air-to-Water ratio) can be tolerated by the plants if this is temporary and very limited in time.

To successfully reduce adverse Air-to-Water ratio it takes, extensive experience, profound horticultural knowledge, understanding the historic developments, seeing environmental/natural facts, and the ability to evaluate natural indicators on existing Green Roofs. 

 

Understanding Green Roof Systems 

As long as humans have cultivated plants they have learned that natural parameters in biology, physics and chemistry are given and everything has to collaborate within these nature’s laws. Although we are able to Gen-manipulate plants for better yield, more pest resistant, and for more stress resistance, but the nature’s laws won’t change.

An increasingly number of stormwater professionals recognize that Green Roofs are an excellent, the least expensive and most natural stormwater management tool with many added values for the environment we live in.  However, as often we talk about Green Roofs as often these specialized professionals forget about the Quarterbacks or key players of such systems: the plants!

It is a simple fact that the more we do for healthy plants with a natural diversity, the better a Green Roof system can retain and detain stormwater.   

Within the development of modern Green Roof technology over the last 50 years most Green Roof systems are built with different continues layers.

The basic layers are (from roofing up): Green Roof System -typical

 

  1. Protection layer to separate between roofing and green roofing trade and to protect the underlying components.
  2. Soil/Media extension layer (often described as drainage layer) to mimic natural soil profiles and avoid anaerobe conditions in rooting zone.
  3. Filter layer that avoids fine particle migration within the system.
  4. Engineered Growth Media or soil that meets parameters of FLL*.
  5. Vegetation.  

 

INFO! Trays, pre-planted containers or modular systems try to mimic the same layers within a small defined area like a plastic box, metal container or soil filled bags. These systems are solely made for easy shipping which is blink of eye in the life span of a Green Roof. These systems are not continuously installed and so these systems are considered as a temporary solution for a limited time (5-8 years).  In most cases these planters or trays are getting re-planted or removed over time, many already ended up on landfills.

 

Understanding Green Roof Plants

Because of the highly fluctuating Air-to-Water ratio, experienced Green Roof designers prefer utilizing hardy plants. Ideally plants that can cope with no irrigation, that are more resistant to drought and temporary extensive water, that are more heat and wind tolerant, and vegetation that can fast regenerate after stress.

In most cases and on shallow extensive Green Roofs succulent type of plants (like Sedums) are often the preferred and common choices.  Even so the Sedum family is very large, colorful and low growing, for enhanced resilience they also rely on competition with other plant species like mosses, perennials or grasses of comparable hardy properties. Horticultural experts call this “natural plant diversity”. Such natural plant diversity stands in a full contrast to Sedum monocultures that often come with tray (modular) systems or systems with pre-vegetated mats. Pre-cultivated systems are very popular in North America where instant gratification and more revenue play a pivot role.

The variety of different plant families or allowing a natural diversity increases root activity within the Green Roof system, creates healthy rooting space, soil structure and texture, with desired micro and macro pores for enhanced soil biology, all resulting into a more ideal Air-to-Water ratio, better water retention and increasing stormwater detention.

Understanding the Current Green Roof Industry

With the focus and current trend on stormwater management, it is “natural” that many people try to improve the stormwater managing ability of Green Roofs. In this regard the Green Roof industry is not getting tired in developing a deluge of products and components that are supposed to help with stormwater management, stormwater retention, stormwater detention, stormwater neutralization, and stormwater clarification. Unfortunately most of them are forgetting about the champions; the Plants!

Interestingly many of these innovators are often highly decorated with desirable titles, have done a lot of commercial reductionist research, micro- and selective-research over a short time with floods of data, have written a lot papers that are piling up in the cloud, and they have introduced new words or terms that sound fancy, makes them look trendy or educated.

 

Learn From Common Sense

Our ancestors preferred Green Roofs as an extension of living green and private recreational space, for growing supplemental food or for building protective purposes. Today’s trend moves away from insulating purposes (because that was wrong in the first place) to stormwater management. Environmental aspects go under in the craving for a Return-of-Investment (ROI). With an entire Armada of specialty Green Roof products, with an army of engineers, and a deluge of data people are trying to narrow-down a living machine (a.k.a. Green Roof) into a static, man-made tool by altering, avoiding or eliminating natural processes which are elementary for healthy and resilient survival of plants/vegetation. It is like feeding less to livestock to reduce Methane gas emissions.    

Some of the problematic and counterproductive specialty Green Roof products are:

  • Very thick layers of synthetic fabrics with increased retention and/or detention capacity based on internal capillarity properties or hydrophilic properties. These specialty fabrics often reverse natural capillarity of engineered soils what dries out the soils faster or when infiltrated with organics particles there is waterlogging and rotting.

  • Some Retention and Detention/Drainage Boards (mainly made from plastic) have no time-release overflow or no overflow that allows air between the water reservoirs. Not talking about polystyrene plastics that are bad for the environment in all regards.

  • Water Crystals, Hydrogels are small chunks (or crystals) of man-made, water-absorbing polymers. The chunks are like sponges – they hold a tremendous amount of water by increasing in size. The liquid is then supposed to release gradually into the soil.  These products have a limited lifespan that is generally less than 1/10 the lifetime of a Green Roof and so not worth the investment.

  • Mineral Wool is a manmade material from glass fibers either spun together or adhered together. Beside that mineral fibers are a possible human carcinogen these specialty products support an Air-to-Water ratio from 95/5 to 5/95 (95% water/5% air to vice versa) whereas the strong water holding capacity /waterlogging is much longer than in natural soil profiles and creates temporary anaerobe conditions = water stress on succulent type plants and root rot.
  • High organic content (over 50%) in growth media (soil). Decomposing of organic matter increases biology activity which is related to heat, causes unusual nutrient increase or decrease, and an increase of carbon dioxide in the soil profile. This and the additional risk of waterlogging increase the stress on plants.
  • Slow release or fast release, solid or liquid fertilizers of synthetic/chemical origin behave on extreme locations like roofs very different to on-grade applications. Especially in combination with the above specialty products there could be a serious and snowballing risk for the vegetation and the environment through run-off. It can increase salt concentrations or chemical process that cause deterioration of other components (e.g. roofing) of the Green Roof or the structure.
  • Chemical weeding Chemical weeding is a common practice mostly used in North America where environmental laws and standards are very low. Chemical on extremes locations behave very different to on-grade locations and succulent type of plants that have a slower metabolism what means they might die very slowly. What looks like chemical “resident” may be affect such plants years later, weakens them and exposes them to other diseases easier.


Conclusion

Vegetation placed on ground remote or ground disconnected location is a century-old tradition for very different and combined purposes. Optimizing only the aspect “stormwater” will ultimately affect all other natural cycles within a Green Roof system. Especially in North America these considerations for natural cycles on a Green Roof are often not known, disregarded or purposeful ignored for a desperate craving of profit and ROI.

This might looks like a society accepted approach but it can result that Green Roofs in North America might not get as popular and as accepted as in European countries where commons sense, decades of monitoring, fundamental education, and solid experience is the driver for their success. Most countries in Europe understand that healthy driven plants, plant diversities and plant communities on roofs increase the benefits as they progress, develop, and generate a natural ecosystem.

End

Mineral Wool in Green Roofs – From Zero to Hero?

Green Team at Green Roof Technology, - Saturday, April 13, 2019

 Mineral Wool in Green Roofs – From Zero to Hero?

The use of Mineral Wool in Green Roof applications is an increasing trend in North America and in countries where such industry is still young or focused on fast profits rather than on longevity.

 

One selling benefit of Green Roofs is the extended lifetime of the underlying water proofing because the Green Roof protects the roofing against the elements. Can Mineral Wool stand up to this?

Against any semi scientific promotional material from Mineral Wool applicators, the market share of mineral wool in the German Green Roof construction industry is around 0.1% or out of 100 million square foot new green roof construction every year (Germany) it is only around 100,000 sf/year.

The reasons for this marginal market share are simple:

  • Mineral Wool has shown a drastic loss in performance after 5-7 years.
  • Mineral Wool is engineered for nurseries and for only one growing cycle.
  • Mineral Wool fibers are considered “hazard” in Europe.
  • On extensive Green Roofs the water retention and water-air ratio is unsuitable for succulents.
  • Mineral Wool expands and contracts in wet-dry cycles.
  • Mineral Wool is hydrophobic and can dry out the traditional overlaying growth media faster.
  • Mineral Wool growth media boards require ballast.
  • Green Roofs with Mineral Wool are difficult to repair, replant or recover.
  • Mineral Wool interrupts natural soil profiles (unnatural soil profile).
  • Mineral Wool is an additional installation step and related to higher costs.
  • Some Mineral Wool products compress under the load of ballast (soil).
  • Some Mineral Wool products contain Phenol resin or Phenol-Urea-Formaldehyde resin as binder and these products can hardly be recycled. Ecose technology is environmentally better but it doesn’t eliminate other problems mentioned here.
  • Reuse of all types of Mineral Wool for the same purpose is only possible after a (non-existing) difficult remanufacturing process.

 

An inexperienced green roof installer might like the idea of an obvious simple installation. However, what looks nice in a brochure doesn’t necessarily reflect the reality. Ballast on the Mineral Wool boards is still required and this requires different equipment. The setup costs for additional equipment are the same whether small or larger amounts of ballast ( or ballast reduces the setup costs).

Engineers might like the tremendous amount of water retention of Mineral Wool. However, they forget that plants (vegetation) have a very specific need for a balanced air-water ratio. If engineers plan the use of succulents (like Sedums) such air-water ratio is even more important (emphasis on air). Engineers are not horticulturalists.

Mineral Wool is widely used in nurseries for one-season vegetables. After this growing season the Mineral Wool (often combined with plastic) ends up on landfills. In 2008 it was around 200,000 tons of hazard waste in Netherland alone. Further, nurseries are growing their crops under highly computer controlled conditions for nutrients and air-water ratio in green houses. Who wants to sell a nursery to a building owner with roof under the sky?

In general shouldn’t we like Mineral Wool in Green Roofs? Mineral Wool gives us lucrative additional jobs in the future for repair or replacement (job security…).

 

 Photo: Repair, Reuse - impossible

I am a lifelong green roof professional and I stand up to my principals with the promise that a green roof should last as long as the building – and that the materials can be reused for the same purpose after that and without processing (there are many fancy names in advertising for it, like cradle-to-cradle etc.).

Like me many people don’t care about fancy word creation and they stand for and what the American Green Roof industry should stand for uncompromised quality and doing things right. Quick profits, instant gratification or senseless warranties don’t promote the trade of professional Green Roofers and it is certainly not my philosophy.

Mineral Wool is: From hero to zero.

 

I appreciate reading my opinion, based on 4 decades of Green Roof experience from all Green Roof friendly places in the world.

World’s First Modular Green Roof System

Green Team at Green Roof Technology, - Sunday, February 12, 2017

World’s First Modular Green Roof System

Modular Green Roof System

Green Roof Professionals around the globe often wonder or speculate how and when the commercial modern Green Roof industry really took off. There are many opinions and alternative facts out there but only a few really know that the hot spots with patents were in Basel Switzerland and in Stuttgart Germany for seamless or wall-to-wall Green Roof systems.

The World’s first modular (or tray) system has been developed in Stuttgart by Brecht and Hämmerle, mainly known as the Brecht System (if one doesn’t consider terracotta pots on roofs as a modular system).

The Brecht System was a basic polystyrene box with a three-layer Green Roof system. The system was available in extensive, semi- intensive and intensive planting depth. With this simple three-layer system the inventor combined many benefits in one box. All systems had a water reservoir for maximum water retention – more than any other Tray system currently on the market and more than any fabrics, foams or mineral wools, and the boxes contained standard nursery soil for a healthy fast growth and to lower costs.

There were different options for covering the less attractive boxes, with either wood or metal (aluminum). Today we call these frames around the boxes: Edging.  

Based on the polystyrene, the boxes were very lightweight and easy to install. Actually, they fitted into each other to create different heights and different planting depths. I would describe them as a Modular –LEGO-like planting system.

Unfortunately, any polystyrene as a limited lifespan when exposed to UV or biological activity and so many of these roof gardens had problems after 5-10 years. Further, many of the plants rooted out of the boxes (drainage holes) and penetrated the waterproofing.

Around 1992 the last Brecht System was removed and replaced by wall-to-wall or seamless Green Roof systems. All of these Green Roofs are still existing - if the building still exists.

The Brecht Modular Green Roofs system had also other issues that are similar to the currently existing systems. However, nowadays the tray systems use metal, other plastics, and mainly with irrigation systems. This makes them last longer, but as often only delays the point of failure. The roots of plants and the biological activity on healthy Green Roofs are often underestimated as well as the functional lifespan of foams, polystyrene drainage mats, and mineral wool products.

The Best Green Roof System

Green Team at Green Roof Technology, - Saturday, August 01, 2015

The main purpose of an extensive Green Roof is stormwater retention and delaying stormwater runoff amongst many other added values.

Above: An Irrigated thin layered Green Roof System – without irrigation it would be dead.

In the last decade in North America, we've seen many Green Roofs where the intended plants never really flourished. I estimate that in the US at least 50% of the green roofs are not performing to their fullest potential. This can be observed by simply looking at the most obvious of indicators, the plants themselves, regardless if they were planted on purpose or somehow found the space to take root. 

Most of these less healthy extensive Green Roofs are thin-layered systems, pre-planted boxes (often called modular systems or hybrid systems), Green Roof Systems from roofing manufacturers with ineffective components, single source warranty-systems, or design intents without consideration for the needs of plants. Typically these systems much more costly (whether thin or thicker) and the mid to long term results are often far below systems that are assembled in place with common sense.

 

Thin-Layered system with irrigation - doesn't work and doesn't retain much water

We all know that the transition from being a common nursery-grown plant (including pre-planted boxes) to the extreme environment of a rooftop poses severe challenges. Green roof plant nurseries typically have "great" advice and recommend the installation of temporary or permanent irrigation systems. In some areas this might be helpful when operated correctly but in all cases this advice is defeating the purpose of an extensive Green Roof (water retention). In almost all cases any type of irrigation caused a spiral of failures and it is wrong to irrigate extensive Green Roofs in areas with limited water for the cause of just having a green roof (Green Washing). Most company sponsored experts don’t see the entire picture or they only see the short term profit and commission (“Mow-Blow-Go”).

If a problem occurs and since many Green Roof system developer lack the proper and specific green roof horticultural knowledge, they may not be able to identify problems by simply looking at the indicators (the plants). This could cause the problem to gain momentum. In addition, the false conclusion that technology (Google search, Apps, synthetic growth media or sophisticated soil moisture control devices) can fix the problem supports my theory of hardly experienced or misinformed green roof professionals. They rely heavily on technology to fix any issues and miss the big picture.

Nature has the ability to take care of itself, as long as the appropriate design, materials and plants are used in addition to being familiar with the immediate location and climate.

Thin layered, super lightweight systems or systems with “innovative” components are just by physics not meant to retain “more” stormwater for the plants or they retain too much water for specific plants. As a matter of fact the costs for retaining stormwater in thin layered systems are extremely high comparing to a standardized extensive Green Roof with a thickness of 4-6 inch (depending on location). Besides the initial costs the lack of water retention (don’t forget all studies are done by the companies!) won’t support any significant bio diversity plus the operational costs (because of the required irrigation) are tremendous over time. Typically these Green Roofs never pay back with they are not utilized for “Green Washing” purposes in advertising.  

Irrigated extensive Green Roofs and/or thin layered, super lightweight systems (below 25 lbs/sf) will increase the nutrient pollution in runoff, require higher fertilization application, have hardly any tendency for self-healing, and may increase the pressure of unwanted plants and have a high risk for failure. Irrigated extensive Green Roofs are not environmentally friendly in most loactions!

Green roof designers and green roof professionals must understand that certain advertising, studies, White Papers or project references are all assembled by specific manufacturers and their goal is to make money – unfortunately on the back of a very advanced technology and on the back of their clients.

When we advise our clients they get the full picture because we have seem all solutions in the last 35 years, we have tested them and we are currently working millions of square feet where these systems require upgrades, reinstallation or massive repair (around 20 million in damage so far).

We also help our clients doing it as efficient as possible and to get their money back from prior failures through warranty claims and sophisticated lawsuits. This might help to standardize the function of Green Roofs and helps to get the black sheep out of the market. The building owner has a right that things are done right from the beginning.

Never irrigated in the last 10 years.

Mineral Wool on Green Roofs

Green Team at Green Roof Technology, - Sunday, September 21, 2014

 Green Roof Innovation

 Mineral Wool on Green Roofs

 Green Roof Technology Reveals Latest Study about Mineral Wool on Living

Since their first commercial production in 1871 (Georgmarienhütte, Germany), mineral wool found its way in many applications like thermal insulation and soundproofing. Mineral wool, mineral fibers are typically referred to synthetic materials like fiber glass, ceramic fibers and stone or rock wool.

Two main types of mineral wools are on the market – water repellent (Hydrophobic) and water adsorbent (Hydrophilic). For horticultural purposes, only the hydrophilic type is useful. Many patents were granted for simple Hydroponic systems or the germination of seeds with mineral wool in the early 80’s.

In modern green roof technology the first green roof systems came on the market around 1985 in Germany at a time as the German green roof industry gained tremendous momentum. As a lightweight solution with high water retention, mineral wool seemed an ideal material. The higher costs and the higher carbon footprint - comparing to lightweight aggregates – were argued with easier installation and higher water retention.

Extensive research over more than 5 years at the University of Geisenheim and on numerous buildings confirmed the high water retention properties. However, in the mid-run these tests also revealed that the performance and the health of the vegetation were far below conventional green roof systems with standardize green roof components. Mineral wool manufacturers and green roof system suppliers stepped away from the idea of using mineral wool as a growing component for green roofs.

“Today we can see a revival of mineral wools in the green roof industry,” says Jorg Breuning, CEO, Green Roof Service LLC,” in countries with hardly any green roof experience, mineral wool is getting rather popular with potentially fatal results in the mid and long-run.” 

Especially in the United States, the market is growing rapidly for mineral wools on green roofs, disregarding existing studies and without extensive long-term tests. It isn’t even proven whether certain fibers can cause health problems, leach out chemicals or whether these components can be recycled when the green roof doesn’t perform anymore.

In 2012, the lack of performance of mineral wool as a vegetation carrier resulted in a major green roof restoration at Amsterdam International Airport. 90,000 square foot of green roof – built with mineral wool - had been taken off and replaced by a standardized green roof system. At this point, this was the largest green roof restoration in the history of mineral wool on green roofs. Costs that could have been avoided.


Doing it right in the first place.

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